The present invention relates generally to engine hydraulic systems used for fuel injection and exhaust/intake valve actuation, and in particular to such systems having variable timing valve actuation.
Engineers are always searching for ways to improve the efficiency and performance of internal combustion engines. In many internal combustion engines, gas exchange valves and the fuel injection system are driven with a rotating cam coupled directly to the engine crankshaft, necessarily linking the timing and duration of fuel injection and gas exchange to engine speed and crank angle. However, engineers have recognized that combustion efficiency and overall engine performance can be improved by de-coupling this linkage of the fuel injection system from the rotation angle of the crankshaft.
Caterpillar, Inc. of Peoria, Ill. has seen considerable success by incorporating hydraulically-actuated electronically-controlled fuel injectors into engines. In such engines, an engine computer is used to control injection of a calculated amount of fuel into the combustion space in a timing scheme based upon sensed operating conditions and other parameters. Caterpillar, Inc. has also developed an engine in which the timing and duration of both fuel injection and gas exchange valve actuation are de-coupled from the engine crank angle. An example of this engine can be found in U.S. Pat. No. 5,957,106 issued to Maloney et at. on Sep. 28, 1999. The Maloney engine utilizes a gas exchange valve integrated with a fuel injector in which the fuel injection mechanism is housed partially within the gas exchange valve member. Because both fuel injection and gas exchange are electronically controlled, actuation of both subsystems can be accomplished independent of the position of the engine""s crank shaft.
While this innovative design has promise, the merger of gas exchange actuators with fuel injector structure is relatively complex. Additionally, the gas exchange valve member is limited to moving between two positions, reducing the desirability of the design for applications in which multiple valve positions are desired. Furthermore, the hydraulic force provided for valve actuation may need modification to open the valve against the gas pressure in the cylinder when the piston nears its top dead center position to perform compression release braking. Due to this issue, Maloney may need design changes to be better suited for engine compression release braking, in which the valves must be quickly opened and closed against substantial pressure in the cylinder. The present invention is directed to solving one or more of the problems set forth above.
In one aspect, a hydraulic system is provided which includes a pump with an outlet, a low pressure drain, a high pressure rail, and a fuel injector fluidly connected to the high pressure rail. A gas exchange valve actuator is also provided, and a timing valve which has an off position and an on position. In the timing valve""s off position, the outlet of the pump is fluidly connected to the low pressure drain. In its on position, the pump outlet is fluidly connected to the gas exchange valve actuator. A supply line is also provided which fluidly connects the output of the pump to the high pressure rail.
In another aspect, the present invention includes a method of operating an engine. The method includes a step of opening a gas exchange valve at least in part by fluidly connecting a gas exchange valve actuator to an outlet of a pump at a first time. The method also includes the step of supplying fluid to a high pressure rail at least in part by fluidly connecting the outlet of the pump to the high pressure rail after the gas exchange valve is opened. The method further includes the step of injecting fuel at least in part by supplying fluid to a fuel injector from the high pressure rail at a second time.
In still another aspect, the present invention includes an engine comprised of an engine casing defining a plurality of cylinders. Attached to the engine casing is a fuel injector, at least one gas exchange valve actuator, a pump, a supply line, and a timing valve for each of the plurality of cylinders. A low pressure drain and high pressure rail are also provided. Each timing valve has an off position in which an outlet of the pump is fluidly connected to the low pressure drain, and an on position in which the outlet is fluidly connected to the gas exchange valve actuator.